Automatic flight control with pilot fly-through

Abstract

A system and technique is disclosed which enables an aircraft to naturally respond to pilot inputs during automatic flight control of aircraft attitude or course and to smoothly return to that attitude or course following pilot maneuvers. The aircraft attitude control channels of an aircraft control system are held at a predetermined attitude reference by an automatic flight control system or programmed to follow a particular navigational course by a flight director guidance system. The aircraft control stick is coupled to disconnect the predetermined pitch and roll attitude from flight control following a stick movement of a predetermined distance or the application of a predetermined force to the stick so that the AFCS or flight director guidance system no longer attempts to hold the set attitude or navigational course. The control stick commands an angular rate of change proportional to the magnitude of the pilot's stick displacement or force. Upon release of the force and return of the aircraft control stick to a neutral position, a "fly through" fading circuit smoothly returns the aircraft to its original attitude or navigational course.

What is claimed is: 
     
       1. An aircraft attitude control system comprising: means for receiving a signal representing a preset aircraft attitude;   means for receiving a signal representing actual aircraft attitude;   means for combining said signals to provide an error signal as a control output during a first control mode for automatically controlling said aircraft attitude so that said actual aircraft attitude is equal to said preset aircraft attitude;   means for removing said error signal as said control output during a second control mode and manually substituting a signal as said control output for changing aircraft attitude during said second control mode; and   means responsive to said error signal for developing a profile signal during said second control mode and modifying said error signal with said profile signal upon return to said first control mode, such that said modified error signal returns said aircraft attitude from a changed attitude to said preset attitude in accordance with a predetermined profile.   
     
     
       2. The system of claim 1 wherein said means for receiving said preset aircraft attitude includes a means for receiving and storing a signal representing a constant attitude. 
     
     
       3. The system of claim 1 wherein said means for receiving said preset aircraft attitude comprises a means for receiving a programmed attitude which changes with respect to time. 
     
     
       4. The system of claim 2 wherein said means for receiving and storing further includes means for modifying said stored attitude at a selected time during said second control mode so that it equals instantaneous aircraft attitude at said selected time. 
     
     
       5. The system of claim 1 wherein said means for removing comprises: an aircraft control stick having a neutral position and a displaced position;   means responsive to said aircraft control stick in said displaced position for disconnecting said error signal as said control output upon displacement of said stick by a predetermined amount and providing a signal commanding a constant rate of aircraft attitude change proportional to stick displacement; and   means responsive to said neutral position of said aircraft control stick for providing said error signal as said control output to automatically control said aircraft attitude.   
     
     
       6. An aircraft control system comprising: means for receiving a signal representing a preset aircraft attitude;   means for receiving a signal representing actual aircraft attitude;   means for combining said signals representing preset aircraft attitude and actual aircraft attitude for providing an error signal as a control output for controlling aircraft to maintain actual aircraft attitude equal to said preset aircraft attitude during a first control mode;   means for manually providing a signal for commanding an aircraft attitude change and providing that signal as said control output in lieu of said error signal during a second control mode and resubstituting said error signal as said control output upon return to said first control mode; and   means responsive to said manual means for storing a signal during said second control mode and for modifying said error signal upon return to said first control mode in response to said stored signal such that said modified error signal will cause aircraft attitude to return from a commanded attitude change to said preset aircraft attitude in accordance with a preset profile.   
     
     
       7. A technique for providing pilot fly-through in an automatic aircraft attitude control system comprising: receiving and storing a signal representing a predetermined aircraft attitude;   receiving a signal representing actual aircraft attitude during aircraft flight;   combining said signal representing actual aircraft attitude with said stored signal representing a predetermined aircraft attitude to produce an error signal for automatically controlling aircraft attitude to maintain said predetermined attitude during a first control mode;   manually interrupting said error signal to produce an attitude control signal for changing aircraft attitude during a second control mode and removing said attitude control signal and providing said error signal upon return to said first control mode;   storing a profile signal in response to said manual interruption during said second control mode; and   modifying said error signal upon return to said first control mode in response to said stored profile signal to produce a modified error signal which returns said aircraft to said predetermined attitude following a change in attitude in accordance with a predetermined profile.   
     
     
       8. An aircraft attitude control system comprising: means for receiving a signal representing a preset aircraft attitude;   means for receiving a signal representing actual aircraft attitude;   means for combining said signals to provide an error signal as a control output during a first control mode for automatically controlling said aircraft attitude so that said actual aircraft attitude is equal to said preset aircraft attitude;   means for removing said error signal as said control output during a second control mode and manually substituting a signal as said control output for changing aircraft attitude during said second control mode; and   means responsive to said error signal for developing a profile signal during said second control mode and modifying said error signal with said profile signal upon return to said first control mode such that said modified error signal returns said aircraft attitude from a changed attitude to said preset attitude in accordance with a predetermined profile, said means for developing and modifying comprising dual signal integration loops which are coupled to integrate said error signal during said second control mode to produce an integrated signal and to subtract said integrated signal from said error signal to produce said modified error signal upon return to said first control mode and provide said modified error signal as said control output for returning said aircraft to said preset attitude.   
     
     
       9. The system of claim 8 wherein said dual signal integration loops comprise: a first summing circuit for receiving said error signal at a first input and providing an output;   a first switch having first, second and third terminals and being operable to selectively electrically couple its first or second terminal to its third terminal, said third terminal being coupled to the output of said first summing circuit and said first terminal forming said control output;   a second summing circuit having a first input coupled to the second terminal of said first switch and providing an output;   a first integrator having an input coupled to the output of said second summing circuit and having an output coupled to a second input of said first summing circuit for subtraction from said first input of said first summing circuit;   third summing circuit having a first input coupled to the output of said first integrator and having an output coupled to a second input of said second summing circuit for subtraction from the first input of said second summing circuit;   a second switch having first, second and third terminals and being operable to selectively electrically couple its first or second terminal to its third terminal, said first terminal of said second switch being coupled to the output of said third summing circuit;   a second integrator having an input coupled to the third terminal of said second switch and an output coupled as a second input to said third summing circuit for subtraction from said first input of said third summing circuit; and   an amplifier having an input coupled to the output of said second integrator and an output coupled to said second terminal of said second switch.